1. Field of Invention
The invention relates to a piezoelectric transducer for use in an ink ejector and relates to a method of manufacturing the piezoelectric transducer.
2. Description of Related Art
A piezoelectric ink ejecting mechanism has been conventionally proposed for a printhead. In a drop-on-demand ink ejecting mechanism, a piezoelectric transducer deforms to change the volume of an ink channel containing ink. Ink in the ink channel is ejected from a nozzle when the volume is reduced, while ink is drawn into the ink channel when the volume is increased.
A single piezoelectric transducer having a plurality of ink ejecting mechanisms and disposed across a plurality of ink channels has recently been proposed for a piezoelectric ink ejector. A portion of the piezoelectric transducer corresponding to a particular ink ejecting mechanism is locally deformed. Such a piezoelectric transducer is disclosed in U.S. Pat. No. 5,402,159. The structure and the manufacturing method of the piezoelectric transducer disclosed in that patent will be described below.
As shown in FIG. 12, a piezoelectric transducer 38 is made of ceramic green sheets 40. Inner individual electrodes 44 are formed on a ceramic green sheet by screen printing, and an inner common electrode 42 and its lead are formed by screen printing on another ceramic green sheet. The required number of ceramic green sheets with inner individual electrodes and with an inner common electrode are laminated alternately, and another green sheet without electrodes is laminated on the top. The laminated ceramic green sheets 40 are thermally pressed, degreased, and sintered as required. Then, an outer common electrode 52 is attached to the leads of the inner common electrodes 42, while outer individual electrodes 54 are attached to the exposed portions of the inner individual electrodes 44.
Thereafter, the piezoelectric transducer 38 thus obtained is immersed in an oil bath filled with an insulating oil, such as a silicon oil, heated to a temperature of about 130° C., and the piezoelectric transducer 38 undergoes polarization. An electric field of about 2.5 kV/mm is applied by a polarizing power source 56 to the outer common electrode 52 and the outer individual electrodes 54. As a result, polarization electric fields are generated at those areas of the ceramic sheets 40 that are sandwiched between the inner individual electrodes 44 and the inner common electrodes 42, and these areas are polarized. The piezoelectric transducer 38 is attached across a plurality of ink channels such that the inner individual electrodes 44 on each ceramic sheet 40 correspond in a one-to-one relationship to the ink channels. Each of the polarized areas, provided over an ink channel, will be deformed when a drive voltage is applied thereto.
Because the piezoelectric transducer 38 is manufactured by unitarily pressing and sintering the ceramic green sheets 40 formed with inner electrodes 42, 44, the ceramic green sheets 40 are likely to vary in thickness among piezoelectric transducers manufactured, or the inner individual electrodes 44 are likely to vary in area in a piezoelectric transducer manufactured.
By the conventional method, however, the same polarization voltage is applied to all the areas to be deformed of the piezoelectric transducer 38, regardless of variations in finished dimensions of the individual electrodes 44 and the ceramic sheets 40. Thus, the areas to be deformed are polarized to have different piezoelectric characteristics, and when a constant drive voltage is applied to the areas to be deformed, these areas are deformed by different amounts and an ink droplet is ejected at different velocities from the corresponding ink channels.
The forgoing problems could be solved, for example, by changing the drive voltage for each area to be deformed, but this method would increase the costs of a power source or a driving circuit board.